In order to normally operate a rotary machine unit equipped with a rotary shaft, it is important that the rotary shaft is appropriately centered. A technique to appropriately center the rotary shaft has been conventionally known as described in, for example, Patent Documents 1 and 2. In Patent Document 1, at the time of assembling a motor/generator, a rotor is guided to an appropriate position by a centering guide arranged at a stator; thereby, a rotary shaft connected to the rotor is appropriately centered. Also, a screw compressor of Patent Document 2 can be assembled in a state where a rotary shaft is surely centered by a centering guide arranged between a motor and a compression portion.